EFFECT OF PROCESS VARIABLES Flashcards
substances that are made up
of long chains of repeating molecules
❖Polymers
As temperature increases, the molecules of
the polymer move __________ and their kinetic
energy ________. This can cause the
polymer to _____________, and its shape to change.
faster , increases , expand
❖At high temperatures, certain polymer chains
may _________________, resulting in a
loss of material.
break down and degrade
This can lead to a reduction
in the strength and durability of the polymer.
break down due to the high temperatures
Solid polymers that tend to form
ordered regions are termed
crystalline polymers
Polymers that have no crystals at
all are called
amorphous
A real polymer is never completely
crystalline, and the extent of
crystallization is characterized by
the percentage of __________________
crystallinity.
Difference between the chart of amorphous and crystalline
- amorphous no flexible crystalline part
- amorphous no liquid melting
- Crystalline no glassy
(image 5)
In the amorphous region of the polymer,
at lower temperature, the molecules of
the polymer are in
frozen state
In the amorphous region of the polymer,
at lower temperature, the molecules of
the polymer are in frozen state, where the
molecules can vibrate slightly but are not
able to move significantly.
glassy state.
In this state, the polymer is brittle, hard
and rigid analogous to glass.
glassy state.
shows hard, rigid, and
brittle nature analogous to a crystalline
solid with molecular disorder as a liquid.
glassy state.
When the polymer is heated, the polymer
chains are able to wiggle around each
other, and the polymer becomes
soft and
flexible similar to rubber.
State when polymer is heated, the polymer
chains are able to wiggle, and the polymer becomes soft and flexible
rubbery state.
The temperature at which the glassy
state makes a transition to rubbery state
glass transition temperature
Tg
diffuse transition zone between
the rubbery and liquid states for
crystalline polymers, temperature at
which this occurs
flow
temperature, Tf
The glass transition temperature is the
property of the amorphous region of the
polymer, whereas the crystalline region is
characterized by the
melting point
temperature, Tm.
Factors Affecting the Glass
Transition Temperature
on the mobility and flexibility
- Intermolecular Forces
- Chain Stiffness
- Cross-Linking
- Pendant groups
a. Bulky pendant groups
b. Flexible pendant groups
- Plasticizers
- Molecular Weight
ease of the chain segment to rotate along
the chain backbone
flexibility
If the polymeric chains can move easily, then the glassy state can be converted to the rubbery state at _____________, that is, the glass transition temperature is _____________
lower temperature
lower
effect of this: mobility of the chains is restricted, then the glassy state is more stable, and it is difficult to break the restriction causing the immobility of the polymer chains at the lower temperature, because **more energy is required to make the chains free. **
glass transition temperature is raised
Strong intermolecular forces cause
higher
Tg
For example, PVC (Tg = 80 ∘C) has
stronger intermolecular forces than
polypropylene (Tg = −18 ∘C) because of the
_________________________ from the C—Cl bond.
dipole–dipole forces
The presence of the stiffening groups (such
as amide, sulfone, carbonyl, p-phenylene
etc.) in the polymer chain _________________ of the chain, leading to higher glass transition temperature.
reduces the
flexibility
polyethyleneterephthalete is stiffer than
polyethylene adipate due to the presence of _______________. Therefore, Tg value is _____________ for polyethyleneterephthalate.
benzene ring
higher
The cross-links between chains** restrict
rotational motion**
Raise the glass transition temperature
higher cross-linked
molecule will show _____________
than that with
lower cross-linked molecule
higher Tg
the presence of bulky pendant group, such as a benzene ring, can restrict rotational freedom, leading to
higher
glass transition temperature.
As in polystyrene,
the presence of _________________ increases the Tg
benzene ring
the presence of flexible pendant groups, limits the packing of the chains and hence
____________the rotational motion, tending to less Tg
value.
increases
example of Flexible pendant groups
aliphatic
chains
In** polybutylmethacrylate, **the presence of
large aliphatic chain __________________ when
compared with that of polymethylmethacrylate
reduces the Tg value
ow molecular weight
and non-volatile materials added to
polymers to increase their chain
flexibility
Plasticizers
Plasticizers reduce the
intermolecular cohesive forces
between the polymer chains, which in
turn
decrease Tg
Tg
is ___________ with
the molecular weight.
increased
The modulus of a polymer ________ with
increasing temperature.
decreases
As the temperature is increased to a level that
can induce some form of molecular motion, a **relaxation process **follows and there is a drop in
modulus.
The decrease in modulus is due to the normal reduction in ___________ that occurs
with an increase in temperature
intermolecular forces
are materials made up of long chains of repeating units
Polymers
When pressure is applied to a polymer, it can cause the chains to become ___________, leading to an increase in
density.
more tightly packed together
defined as the pressure exerted by a fluid
at equilibrium at any point of time
due to the force of gravity
Hydrostatic pressure
Hydrostatic pressure is
proportional to the ____________
measured from the surface as the
weight of the fluid increases
when a downward force is
applied.
depth
pressure exerted by a liquid on a
solid surface
Hydrostatic pressure
also known as modulus of
elasticity
elastic modulus
unit of measurement of an
object’s or** substance’s resistance to being
deformed elastically** (i.e., non-permanently)
when a stress is applied to it.
elastic modulus
measure of a material’s
**stiffness or resistance to deformation **under an
applied load
elastic modulus
ratio of the change in** length or volume of a material** to the change in length or volume of the applied load
elastic modulus
a stiffer material will have a ________ elastic
modulus.
higher
elastic modulus has the form
𝛿 = STRESS/ STRAIN
force causing the
deformation divided by the area to which the
force is applied
stress
ratio of the
change in some parameter caused by the
deformation to the original value of the
parameteR
strain
describes tensile and compressive
elasticity, or the **tendency of an object to deform along an axis **when opposing forces are applied along that axis
Young’s modulus (E)
defined
as the ratio of tensile stress to tensile strain.
Young’s modulus (E)
often referred
to simply as the elastic modulus
Young’s modulus (E)
Types of elastic modulus
- Young’s modulus (E)
- shear modulus or modulus of rigidity (G)
- bulk modulus (K)
- Flexural modulus (Eflex)
describes an object’s tendency to shear (the deformation of shape at constant volume) when acted upon by opposing forces
shear modulus or modulus of rigidity (G)
; it is
defined as shear stress over shear strain
shear modulus or modulus of rigidity (G)
part of the derivation of viscosity.
shear modulus
describes volumetric elasticity, or the
tendency of an object to deform in all directions when uniformly loaded in all directions
bulk modulus (K)
it is defined as** volumetric
stress over volumetric strain** and is the inverse of
compressibility.
bulk modulus (K)
an extension of Young’s
modulus to three dimensions
bulk modulus (K)
describes the object’s tendency to flex
when acted upon by a moment
Flexural modulus (Eflex)
Elastic modulus of polymers ___________ with increasing
hydrostatic pressure in tension, compression, and
shear.
increases
According to Pae and Bhateja (1975), one of the main reasons for the increase in the elastic modulus with increasing pressure is the effects of ______________
finite
deformations on the polymer.
They claimed that one of the main
reasons for the increase in the elastic modulus with
increasing pressure is the effects of finite
deformations on the polymer.
Pae and Bhateja (1975)
High hydrostatic pressure can cause the glass
transition in a polymer to shift to __________________
higher temperatures
material property and is the stress corresponding to the yield point at which the material begins to deform plastically
yield strength or yield stress
often used to determine the maximum
allowable load in a mechanical component, since it
represents the upper limit to forces that can be applied without producing permanent deformation
yield strength
The yield strength of polymers ____________ with
applied hydrostatic pressure.
increases
When hydrostatic pressure is applied to polymers,
the molecules within the material are forced closer
together, resulting in ______________________.
These increased forces can cause the polymers to
have a __________ yield strength
increased intermolecular forces.
higher
The pressure dependence of the yield strength
usually differs from that of the ______.
modulus
appearance of a crack or complete
separation of an object or material into two or more pieces
under the action of stress
Fracture
The fracture of a solid usually occurs due to the development
of certain _________________ the solid.
displacement discontinuity surfaces within
If a displacement develops perpendicular to the surface, it is
called a
normal tensile crack or simply a crack
if a
displacement develops tangentially, it is called a
shear crack,
slip band, or dislocation
Fracture strength, also
known as
breaking
strength,
stress at
which a specimen fails
via fracture.
Fracture strength
This is
usually determined for a
given specimen by a
tensile test, which charts
the stress
–strain curve
Fracture strength,
The final recorded point in the stress-strain curve
is the
Fracture strength
graph of stress vs strain
(image 30)
Stress vs. strain curve typical of
aluminum
1. Ultimate tensile strength - peak
2. Yield strength - before peak or ultimate tensile strength
3. Proportional limit stress - middle of yield and offset
4. Fracture- end of the graph
5. Offset strain (typically 0.2%) - lowest at y =0
- Ultimate tensile strength
- peak
- Yield strength
- before peak or ultimate tensile strength
- middle of yield and offset
- Proportional limit stress
- Fracture-
end of the graph
lowest at y =0
- Offset strain (typically 0.2%) -
The ___________________ (maximum
stress) of the polymers always increased
with increasing hydrostatic pressure
ultimate tensile strengths
This is attributed on molecular mobility.
ultimate tensile strengths (maximum
stress) & hydrostatic pressure RS
At high pressures, the molecular chains
are forced closer together, decreasing
mobility, so that _______________ are
necessary to produce a given strain
higher stresses
❖ The fracture strength increased
proportionally to the ______________
yield strength
The effect of pressure on
the tensile strength and
________ at break depends
on the polymer
elongation
The tensile strength tends to
increase for __________________
but decrease for some _________________
(similar to elongation)
ductile polymers
brittle
polymers.
In some brittle polymers like
PS, ______________________
is induced beyond a certain
critical pressure
brittle-ductile transition
PE, PTFE,
and PP
most brittle polymers
exhibit cold
drawing at normal pressures.
is a substance that accelerates
chemical reactions without being consumed in
the process
catalyst
reaction that results in the formation of long
chains of polymer molecules.
polymerization process + catalyst
Effects of catalysts in polymerization process
help to speed up
reduce the temperature required
control the structure of the resulting polymer
example of catalysts
enzymes, acids, bases, and
metal ions
a quantity that measures
the extent to which the reaction has proceeded.
Extent of reaction
degree of crosslinking or bonding between
the monomers in a polymer chain.
Extent of reaction
increases the rigidity and strength of
the polymer
Crosslinking
can
affect its flexibility and solubility
extent of bonding
derived a general expression, relating
average functionality (f), extent of reaction (p), and average degree of polymerization 𝑋n
𝑛 for polycondensation reaction
carried out for a period t.
W. H. Carothers
general expression, relating
average functionality (f), extent of reaction (p), and average degree of polymerization 𝑋n
𝑛 for polycondensation reaction
carried out for a period t.
Carother’s Equation
defined as the fraction of
functional groups/monomers that have reacted at time t.
Extent of Reaction (p)
defined as equal to
the **total number of bifunctional initially **added, (No)
, divided by
the remaining number of molecules N after time t
Average degree of polymerization 𝑿n
total number of reacting molecules initially
present
N0
average functionality for the system as
f
The** related functional groups** (say, -OH and –COOH) are
considered to be ___________ in _____________
present , stoichiometric equivalence.
number of molecules present at time t when the extent
of reaction is p
N
number of molecules lost during the process over the
period t
(N0-N);
for each molecule lost, the number of
functional groups lost is
2 (one of each kind)
total number of functional groups lost is ______________against the
initial total number of N0f functional groups
2(N0-N)
initial total number of functional groups
N0f
defined as the
average number of structural units per polymer molecule
average degree of polymerization 𝑋𝑛
very important for
the understanding and control of the growth of polymers
through polycondensation reactions
Carother’s equation
Carother’s equation
image 40
critical extent of reaction at the gel point
pc
implied the formation of essentially infinitely large
polymer network in the reaction mixture.
Gelation
The sudden onset of gelation marks the division of the mixture into two parts
gel
sol
which is soluble in all nondegrading solvents,
the gel,
which remains soluble and
can be extracted from the gel
the sol
As polymerization proceeds beyond the gel point, what happened to the gel?
amount of gel increases at the expense of the sol
As polymerization proceeds beyond the gel point, what happened to the mixture?
mixture rapidly transforms from a viscous liquid to an elastic material of infinite viscosity
ideal gelation
stop the polymerization reaction before the onset of
gelation
can help in determining the critical
extent of reaction at which gelation or cross-linking would commence
Carother’s reaction
theoretical extent of reaction, when the reaction is complete, the polymer being formed in the polycondensation system gets ___________
cross-linked
cross-linked in polycondensation system turns into
insoluble, infusible gelled
mass (undesired)
condensation polymerization
___________ be allowed to proceed beyond point wherein the polymer become insoluble, infusible gelled mass,or otherwise the reaction mass would turn into an ___________________
should not
unusable product
